For questions relating to skating in general, including ice skating, rollerskating and inline skating. For questions more specifically about inline skating, see the [inline-skating] tag.
Skating is an activity where participants use special footwear containing rollers or blades along the sole of the shoe. These "skates" make the wearer glide across a hard surface in a plane parallel to the foot, but resist gliding along any cross plane, thus allowing the wearer to push themselves along by directing force to the side of their intended travel.
There are three main types of skates. Ice skates are the oldest, and have a metal blade with two sharpened edges. These skates can only be used on ice, or an ice-like substitute such as certain polymers. These skates come in many variations and are used for many competitive winter sports such as ice hockey, speed skating, and artistic competitions such as figure skating and ice dancing.
Traditional roller skates have four wheels arranged in a rectangle on two axles. These were originally developed as a substitute for ice skates during warmer seasons and climates. Today, "quad" skates are commonly seen in indoor roller rinks for recreational use, and are also used in roller derby competitions and in certain classes of figure skating.
Inline skates are the newest design, originally developed for use by cross-country skiiers for off-season training. These skates are now used for a variety of sports such as inline hockey (aka roller hockey), stunt and trick performance similar to skateboarding, and recreational long-distance skating for exercise (similar to their original purpose for cross-country skiiers).